Drilling apparatus for hard ground

ABSTRACT

The invention provides apparatus for drilling trenches in the ground, the apparatus comprising a frame and a drilling assembly having a horizontal support plate connected to the bottom end of the frame, said plate supporting drilling tools disposed beneath said plate, said trench being filled with a drilling mud. The periphery of said plate has resilient sealing means for co-operating with the walls of the trench so as to provide at least partial sealing between said plate and the walls of the trench, and means for adjusting drilling mud flow rates from the portion of the trench situated above said plate to the portion of the trench situated beneath said plate, and also in the opposite direction.

FIELD OF THE INVENTION

The present invention relates to apparatus for using a drill to digtrenches in the ground, and in particular in ground that is very hard.

BACKGROUND OF THE INVENTION

Trench drilling apparatuses generally using two drills are well adaptedto making trenches that are deep and of relatively narrow width. Frenchpatent application 2 696 768 describes one such drilling apparatus.However, when the apparatus is required to drill into ground that ishard or very hard, such as stone, conventional machines can be found tobe inadequate. The drills used at present for overburden have a maximumweight of 60 (metric) tonnes. Since such apparatuses are suspended fromthe end of hoisting cables, it is their own weight which is transmittedto the drills in order to perform drilling. Unfortunately, in that kindof ground, it can happen that the load required in order to achieveproper drilling lies in the range 100 tonnes to 150 tonnes, or evenmore. This force depends on the number of tools and the type of toolmounted on the wheels of the drill.

The simplest solution for increasing the weight of the apparatus is toload the frame of the drill. However, that would require a largercapacity hoist to be used and that naturally gives rise to majordrawbacks, particularly concerning site organization.

To remedy that drawbacks, proposals have already been made in Frenchpatent No. 2 749 333 in the name of the Applicant for a particular typeof drilling apparatus that enables trenches to be drilled in hardground.

SUMMARY OF THE INVENTION

Accompanying FIG. 1 is an elevation view of the drilling apparatusdescribed in the above-mentioned document. It comprises a main frame 10which is suspended from the end of a pulley block 12 itself suspendedfrom a jib. The main frame 10 has two vertical main faces, with only thefront face 14 being visible. The apparatus also has a drilling assembly16 that is movable in vertical translation at the bottom end of the mainframe 10. This drilling assembly 16 essentially comprises a supportstructure 18 having a pump 20 mounted thereon to take up the liquid flowentraining the drilled spoil, said pump 20 being connected to a flexibleremoval hose. The drilling assembly also has two rotary cutters 24 and26 secured to drums that are rotated by hydraulic motors fixed to thesupport assembly 18. The support assembly 18 can be moved relative tothe main frame 10 by actuators 28 and 30 which serve firstly to move thedrilling assembly 18 relative to the main frame 10 and secondly to applyadditional force to the drilling assembly when the main frame 10 isanchored in the trench being drilled. To perform such anchoring, themain frame 10 has two shoes, of which only the shoe 32 is visible. Theseshoes can be moved away from the frame, e.g. by means of actuators, soas to anchor the main frame in the trench.

Such a disposition does indeed make it possible to increase the forcethat is applied to the cutters 24 and 26, thereby enabling them to drillinto ground that is very hard. Nevertheless, given the relatively smalldimensions of the active surfaces of the shoes 32 and the large forcethat must be developed in order to anchor the top frame, the pressureexerted by these shoes against the walls of the trench is very high.Providing the trench at the level of the shoes is of a material that isvery hard, such as rock, then such pressure is acceptable. However, ifthe shoes are in a transition zone between relatively soft overburdenthat has already been drilled and rock, it is not possible to use theshoes 32 to develop the force required for achieving effectiveanchoring.

OBJECTS OF THE INVENTION

An object of the present invention is to provide drilling apparatus ofthe rotary cutter type that can be used effectively to drill a trencheven in ground that is very hard and in particular when the ground has alarge transition zone between relatively soft ground and very hardground.

According to the invention, this object is achieved by an apparatus fordrilling trenches in the ground, the apparatus comprising a frame and adrilling assembly having a horizontal support plate connected to thebottom end of the frame, said plate supporting drilling tools disposedbeneath said plate, said trench being filled with a drilling mud, theapparatus being characterized in that the periphery of said plate hasresilient sealing means for co-operating with the walls of the trench soas to provide at least partial sealing between said plate and the wallsof the trench, and means for adjusting drilling mud flow rates from theportion of the trench situated above said plate to the portion of thetrench situated beneath said plate, and also in the opposite direction,so that the pressure of the drilling mud beneath said plate is wellbelow the hydrostatic pressure exerted by the column of drilling mud inthe trench above said plate, and so that the flow of drilling mudextracted from the portion of the trench beneath said plate issufficient to extract the drilling spoil that results from the drillingaction of said drilling tools.

It will be understood that in this embodiment, at least partial sealingis implemented at the plate between the top portion of the trench filledwith mud and the bottom portion of the trench that is being drilledbecause of the presence of the sealing elements at the periphery of theplate. In addition, because of the system for controlling the rate atwhich drilling mud flows in either direction relative to said plate, itis possible to control the pressure of the drilling mud in the portionof the trench that lies beneath said plate. This pressure can thus bemaintained at a value that is relatively low, and of similar order toatmospheric pressure. Consequently, the hydrostatic pressure created bythe column of drilling mud in the portion of the trench above the plateserves effectively to subject the drilling tools to the equivalent of aforce corresponding to the depth of drilling mud. It will be understoodthat the sealing between the plate and the walls of the trench need notbe completely watertight since some leakage flow can be compensated byadjusting the flow rates on either side of the plate.

In an improved embodiment, the drilling apparatus comprises a framehaving two main vertical faces and the drilling assembly is verticallymovable relative to the frame under drive from actuators interposedbetween the drilling assembly and the frame, and it is characterized inthat it further comprises a plurality of inflatable elements secured tosaid main faces of the top frame, and means for injecting a fluid underpressure into said inflatable elements so that the inflatable elementsapply a force between said main frame and the walls of the trench, andmeans for enabling said fluid under pressure to escape from saidinflatable elements so that no force is transmitted between the mainframe and the walls of the trench.

It will be understood that when the inflatable elements are in theinflated state under the effect of the pressure from the fluid, a forceis transmitted between the main frame of the drilling apparatus and thewalls of the trench, thereby providing a force anchoring the top frameto the trench. In this situation, the actuators enable additional forceto be applied to the drilling assembly and in particular to the drillingtools thus enabling drilling to be performed in ground that is veryhard. Naturally, this effect of increasing the apparent weight of thetool of the drilling apparatus is combined with the same effect thatresults from the low pressure beneath the plate of the drilling assemblycombined with the hydrostatic pressure that results from the column ofdrilling mud in the trench above said plate.

DESCRIPTION OF THE DRAWINGS

Other characteristics and advantages of the invention will appear onreading the following description of various embodiments of theinvention given as non-limiting examples. The description refers to theaccompanying drawings, in which:

FIG. 1, described above, shows a prior art drilling apparatus usingcutter wheels;

FIG. 2 is a simplified elevation view of a first embodiment of drillingapparatus of the invention;

FIG. 3 is a view showing a detail of FIG. 2 for a first embodiment ofthe sealing between the plate and the wall of the trench;

FIG. 4 is a view analogous to FIG. 3 showing a second embodiment of thesealing;

FIGS. 5A and 5B are a side view and a front view showing an improvedembodiment of the drilling apparatus of the invention;

FIGS. 6A and 6B show a first embodiment of the inflatable elements forthe apparatus shown in FIGS. 5A and 5B; and

FIGS. 7A and 7B show a second embodiment of the inflatable elements ofthe apparatus shown in FIGS. 5A and 5B.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

As already stated briefly, the invention relies on the principle ofusing hydrostatic pressure from the column of drilling mud in the trenchabove the plate of the drilling assembly for the purpose of increasingthe apparent weight of the tool and thus improving the effectiveness ofthe cutters. For this purpose, at least partial sealing is providedbetween the plate and the wall of the trench by using sealing meansdisposed at the periphery of the plate, and a flow of drilling mud isestablished in one direction or the other through the plate with thisflow being controlled in such a manner that the pressure of the drillingmud beneath the plate is well below the hydrostatic pressure, forexample it can be about atmospheric pressure, and in addition the flowis controlled so as to take place at a rate which is sufficient toextract the spoil that results from drilling implemented by the drillingtools.

A first embodiment of the drilling apparatus is described with referenceto FIG. 2. In this figure, there can be seen the frame 14, the bottomplate 18 having the drilling wheels 24 and 26 mounted on its underside,the pump 20 for sucking out the drilling mud containing the spoil, andthe flexible hose 22 for removing the spoil. The pump 20 is associatedwith a suction nozzle 40 whose openings are located beneath the plate18. The suction nozzle takes in the drilling mud together with thespoil. The figure also shows the trench 42 whose top portion 42 a hasalready been drilled and whose bottom portion 42 b is being drilled. Inthe invention, the bottom plate 18 is fitted around its periphery with asealing gasket 44 that provides sealing between the plate 18 and thewall of the trench 42. Suitable gaskets are described in greater detailbelow. The plate 18 in the particular example described also has twotubes 46 and 48 passing through it to put the top portion 42 a of thetrench into communication with the bottom portion 42 b thereof. Thesetubes are fitted with non-return systems and with means 46′ and 48′ forcontrolling the flow rate passing through them. It will thus beunderstood that the overall flow rate of drilling mud entering andleaving the bottom zone 42 b of the trench can thus be controlled so asto control the pressure in said zone to have some value, e.g. aboutatmospheric pressure. Adjusting the flow rate of the suction pump makesit possible simultaneously to take account of the leakage flow thatexists through the sealing zone. Nevertheless, the drilling mud flowrate must necessarily be sufficient to extract the spoil produced by thecutters 24 and 26.

FIG. 3 shows a first embodiment of the sealing between the plate 18 andthe wall of the trench 42. The periphery of the plate 18 is providedwith a vertical rim 50. A deformable rubber gasket 52 is anchored in theoutside face 50 a of the rim. The gasket 52 is made of rubber and ispreferably hollow so as to be able to comply more effectively withunevenness in the wall of the trench.

FIG. 4 shows a second embodiment of the sealing between the plate 18 andthe wall of the trench 42. The periphery of the plate 18 is likewisefitted with a vertical rim 54 which goes all the way round the peripheryof the plate. This rim 54 has a resilient lip gasket 56 fixed theretowhich likewise goes all the way round the plate 18. The lip gasket 56 isoriented so that the effect of the end of the gasket being pressedagainst the wall of the trench is increased by the column of mud locatedabove the plate 18. To make the drilling apparatus easier to raise afterthe trench has been made, it is preferable to provide lifting bars suchas 58 which can be moved relative to the plate 18 so as to move the freeend of the gasket 56 away from the wall of the trench 42.

In the improved embodiment shown in FIGS. 5A and 5B, the apparent weightof the drilling apparatus is increased by combining the action ofhydrostatic pressure as described above with reference to FIGS. 2 and 4and the action of actuators on the drilling assembly which is then madeto be movable relative to the main frame comprising the top portion ofthe drilling apparatus, with the top frame then being anchored, i.e.prevented from moving in a vertical direction relative to the trench. Asexplained in greater detail below, the anchoring means consist ininflatable elements such as inflatable cushions which are placed on themain faces of the top frame of the drilling apparatus and which, wheninflated, enable force to be transmitted between the top portion of theframe and the facing walls of the trench being dug.

In FIGS. 5A and 5B there can be seen the main frame 14 of the apparatusand the drilling assembly 16 with its plate 18, the drilling assembly 16being movable relative to the main frame 10 under drive from actuators28 and 30.

In this embodiment, inflatable elements such as 64 are fixed to at leasta portion of the main faces 60 and 62 of the main frame 10. By way ofexample, these inflatable elements occupy the entire width of the mainfaces and are placed substantially side by side. Each inflatable element64 is constituted by an inflatable cushion defined by a wall ofelastically deformable leakproof material. Each deformable cushion isfixed via one of its faces 64 a to the main face 60 or 62 of the mainframe, and it is connected to an individual inflation tube 66 in turnconnected to a main inflation tube 68. These tubes can have adjustablepressure limiters for controlling the magnitude of the anchoring force.

To avoid overcrowding FIGS. 5A and 5B, these figures do not show thedispositions that are shown in FIGS. 2, 3, and 4 that enable hydrostaticpressure to act in the manner explained above. The flow rate controlmeans 20, 40, 46′, and 48′ are mounted on the plate 18 of the movingportion. The sealing means 44, 52, and 56 can also be mounted at theperiphery of the plate 18 of the moving portion. It is also possible toprovide a sealing gasket at the bottom end of the main portion of theframe of the machine beneath the inflatable cushions 64, and also toprovide a sealing gasket between the fixed portion of the frame and themoving bottom portion that carries the cutters. In either case,hydrostatic pressure acts on the top face of the moving portion inaddition to the force applied by the actuators 28 and 30.

In this first embodiment, described with reference to FIG. 7A, eachinflatable cushion 64 is covered by a strip 70 of a reinforced rubberyelement whose edges 70 a and 70 b are anchored in the wall 60 of the topframe. This figure also shows one of the walls 72 of the trench beingdrilled. It will be understood that when a fluid (preferably liquid)under pressure is injected into the inflatable elements 64 via the tubes66 and 68, the inflatable element increases in volume and presses thestrip of rubbery material 70 against the wall 72. The pressure thatexists inside the inflatable element 64 then develops a force againstthe wall 72 of the trench that has a horizontal component F which isconverted into a vertical anchoring force F′. It will be understood thatby placing a sufficient number of inflatable elements 60 on the mainfaces, it is possible to obtain a total vertical anchoring force that isvery high without the pressure applied by the inflatable elements viathe deformable strips 70 being high. Thus sufficient anchoring effect isobtained even if the nature of the material in which this portion of thetrench has been dug is of limited strength.

In contrast, as shown in FIG. 7B, when the inflatable element 64 is nolonger under pressure, the strip 70 is moved away from the inside wall72 of the trench and the drilling apparatus can be moved so as to drilla new section of trench.

A second embodiment of the anchoring means are described below withreference to FIGS. 6A and 6B.

These anchoring means are constituted by inflatable elements 64, e.g.comprising inflatable cushions that are identical to those shown inFIGS. 7A and 7B. Each cushion 64 has one of its faces fixed to the wall60, 62 of the main frame and connected to pressurized fluid tubes. Inthis second embodiment, a rigid plate 76 covers the entire surface areaoccupied by the inflatable elements 64 and is secured to the wall 60 viaa hinged link element 78. The link element 78 is constituted by aconnecting rod, for example, or more particularly by a plurality ofconnecting rods disposed above the top inflatable cushion 64 a. It willbe understood that when the inflatable elements 64 are indeed inflated,the rigid plate 76 is pressed against the wall 72 of the trench. Thismakes it possible to obtain high anchoring force while applying onlylimited pressure to the wall of the trench given that it is the plate 76which is of large area that is pressed continuously against the wall ofthe trench.

1. Apparatus for drilling trenches in the ground, the apparatuscomprising a frame and a drilling assembly having a horizontal supportplate connected to the bottom end of the frame, said plate supportingdrilling tools disposed-beneath said plate, said trench being filledwith a drilling mud, the apparatus being characterized in that theperiphery of said plate has resilient sealing means for co-operatingwith the walls of the trench so as to provide at least partial sealingbetween said plate and the walls of the trench, and means for adjustingdrilling mud flow rates from the portion of the trench situated abovesaid plate to the portion of the trench situated beneath said plate, andalso in the opposite direction, so that the pressure of the drilling mudbeneath said plate is well below the hydrostatic pressure exerted by thecolumn of drilling mud in the trench above said plate, and so that theflow of drilling mud extracted from the portion of the trench beneathsaid plate is sufficient to extract the drilling spoil that results fromthe drilling action of said drilling tools.
 2. Drilling apparatusaccording to claim 1, characterized in that said means for adjustingsaid flow rate comprises nozzle-forming means connected to a variableflow rate suction pump for extracting drilling mud from beneath saidplate and means for adjusting a one-way flow of drilling mud from theportion of the trench situated above said plate to the portion of thetrench situated beneath said plate.
 3. Drilling apparatus according toclaim 1, in which the frame has two main vertical faces and saiddrilling assembly is vertically movable relative to said frame underdrive from actuators interposed between said drilling assembly and saidframe, the apparatus being characterized in that it further comprises aplurality of inflatable elements secured to said main faces of the topframe, and means for injecting a fluid under pressure into saidinflatable elements so that the inflatable elements apply a forcebetween said main frame and the walls of the trench, and means forenabling said fluid under pressure to escape from said inflatableelements so that no force is transmitted between the main frame and thewalls of the trench.
 4. Drilling apparatus according to claim 3,characterized in that a strong layer that is movable under the effect ofinflating the inflatable elements is disposed on the face of eachinflatable element that faces towards the walls of the trench. 5.Drilling apparatus according to claim 4, characterized in that saidmoving layer is constituted by a plurality of strips of elasticallydeformable material having edges secured to a main face of the mainframe, at least one inflatable element being interposed between saidstrip and said main face.
 6. Drilling apparatus according to claim 4,characterized in that said moving layer is constituted by a rigid plateconnected to said main face by link means allowing said plate to move ina direction that is orthogonal to said main face, said inflatableelements being interposed between said main face and said plate. 7.Drilling apparatus according to claim 3, characterized in that saidinflatable elements are inflatable cushions made of a material that isleakproof and elastically deformable.
 8. Drilling apparatus according toclaim 2, in which the frame has two main vertical faces and saiddrilling assembly is vertically movable relative to said frame underdrive from actuators interposed between said drilling assembly and saidframe, the apparatus being characterized in that it further comprises aplurality of inflatable elements secured to said main faces of the topframe, and means for injecting a fluid under pressure into saidinflatable elements so that the inflatable elements apply a forcebetween said main frame and the walls of the trench, and means forenabling said fluid under pressure to escape from said inflatableelements so that no force is transmitted between the main frame and thewalls of the trench.
 9. Drilling apparatus according to claim 4,characterized in that said inflatable elements are inflatable cushionsmade of a material that is leakproof and elastically deformable. 10.Drilling apparatus according to claim 5, characterized in that saidinflatable elements are inflatable cushions made of a material that isleakproof and elastically deformable.
 11. Drilling apparatus accordingto claim 6, characterized in that said inflatable elements areinflatable cushions made of a material that is leakproof and elasticallydeformable.